In order to test the electrical characteristics of IC chips consisting of a great number of memory circuits, logic circuits and the other components formed on a semiconductor wafer, a probe card as disclosed in Japanese unexamined patent publication No. 2000-055936 is used as a contactor, for example. This probe card plays a role in relaying test signals that are sent and received between a tester, which is test equipment, and an IC chip upon the probe card makes contact with an electrode pad on the wafer during the test.
This probe card, for example, has a plurality of probe needles corresponding to a plurality of electrode pads formed on an IC chip, and each of the probe needles is brought into electrical contact with each of the electrode pads to perform a test of the IC chip. The probe needle includes a tip for making contact with the electrode pad and a cantilever made of a resilient member.
FIGS. 6A to 6H show a fabrication process of the probe needle, while FIG. 7 is an external perspective view of the probe needle fabricated through the fabrication process of FIGS. 6A to 6H. Referring to FIGS. 6A to 6H and FIG. 7, a description now will be made about a conventional probe needle.
On a surface of a silicon substrate 1 shown in FIG. 6A, a silicon dioxide film 2 is formed as shown in FIG. 6B, and then a resist film 3 is formed on a surface of the silicon dioxide film 2. After being exposed to light with a photomask (not shown), the resist film 3 undergoes a development process to form a quadrangular opening groove 4. The silicon dioxide film 2 just under the opening groove 4 is then removed. After an inverted truncated pyramidal groove 5 is formed by anisotropically wet-etching the silicon substrate 1 as shown in FIG. 6C, the resist film 3 and silicon dioxide film 2 are removed as shown in FIG. 6D.
Further, as shown in FIG. 6E, a titanium film 6, which will be a plating seed, is formed over the entire surface of the silicon substrate 1. Next, a sacrificial layer 7 shown in FIG. 6F is formed by means of a photolithography technique on the titanium film 6 except for an area to be a cantilever 8 and groove 5. Then, as shown in FIG. 6G, a nickel alloy, for example, is deposited, by plating, in the area corresponding to the cantilever 8 and groove 5 but not on the sacrificial layer 7. As shown in FIG. 6H, the sacrificial layer 7 is removed to complete an inverted truncated pyramid 9, which is the tip of the probe needle, and a cantilever 8.
The probe formed through the fabrication process shown in FIGS. 6A to 6H has the rectangular parallelepiped cantilever 8, for example, having a length L of 200 μm to 500 μm, a width W of 60 μm to 150 μm, and a thickness T of 10 μm to 20 μm, and the inverted truncated pyramidal tip 9 having a height H of 50 μm to 100 μm and a width Wt at its top flat part of 10 μm±2 μm, as shown in FIG. 7.
By the way, with the recent increase in the number of components per IC chip, the number of electrode pads has increased and the arrangement pitch of the electrode pads are becoming narrower and narrower. Because of this, the probe needle may touch adjoining electrode pads unless the width of the probe needle is reduced, and it can be said that the probe needle has not been meeting the pitch of the electrode pads. However, reduction of the width of the inverted truncated pyramid 9, which is a tip of the probe needle shown in FIG. 7, requires reduction of its height.
In other words, because the inverted truncated pyramid 9 is formed using the groove 5 that is formed by the anisotropic wet etching as shown in FIG. 6C, the more the diameter of the groove 5 is decreased, the shallower the depth of the groove 5 becomes. On the contrary, in order to deepen the groove 5, the diameter of the groove 5 must be increased, resulting in an increase in diameter of the tip. Such a tip is not applicable to the tendency to narrow the pitch between the electrode pads.
As described above, a height-reduced inverted truncated pyramid 9 may cause the cantilever 8 to touch the electrode pads and other components or may prevent itself from appropriately making contact with the electrode pads. In addition, the short inverted truncated pyramid 9 may cause the cantilever 8 to bend and thus touch the electrode pads.